Ion implanters are widely used in device fabrication, including semiconductor manufacturing to control device properties. In a typical ion implanter, ions generated from an ion source are directed as an ion beam through a series of beam-line components that may include one or more analyzing magnets and a plurality of electrodes that provide electric fields to tailor the ion beam properties. The analyzing magnets select desired ion species, filter out contaminant species and ions having undesirable energies, and adjust ion beam quality at a target wafer. Suitably shaped electrodes may modify the energy and the shape of an ion beam.
For high energy implantation, typically 300 kV or greater, tandem acceleration is often used to generate ions of the required energy. Often tandem acceleration is applied to ions such as hydrogen ions in order to generate sufficiently high energy for ions to implant to a desired depth into a substrate. In a tandem acceleration process, an electrostatic accelerator accelerates negative hydrogen ions generated in a special ion source from ground potential up to a positive high-voltage terminal. The electrons on the negative hydrogen ions are then stripped from the negative ion by passage through a charge exchange region, and resulting positive hydrogen ion (proton) is again accelerated as it passes to ground potential from the high negative potential. The protons emerge from the tandem accelerator with twice the energy of the high positive voltage applied to the tandem accelerator.
One problem encountered when producing high energy hydrogen ion beams for ion implantation is the relatively low ion current, which may limit throughput of substrates to be implanted with high energy hydrogen. For example, in commercial power device fabrication it may be desirable to implant hydrogen at ion energies of up to 1.5 MeV and currents of 0.25 mA or higher, which is difficult to obtain using conventional ion implanters. In view of the above, it will be apparent that improvements in high energy proton beam current are needed.